Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.85   11.733%   $211.0078   $211.01   $211.00   $211.00  
  Purchase #2 $170.94   3.463%   $176.8597   $176.86   $176.85   $176.90  
  Purchase #3 $120.56   3.872%   $125.2281   $125.23   $125.25   $125.20  
  Purchase #4 $244.27   11.695%   $272.8374   $272.84   $272.85   $272.80  
  Purchase #5 $78.62   10.157%   $86.6054   $86.61   $86.60   $86.60  
  Purchase #6 $35.55   3.115%   $36.6574   $36.66   $36.65   $36.70  
  Purchase #7 $39.28   6.376%   $41.7845   $41.78   $41.80   $41.80  
  7 purchase totals = $878.07       $950.9803   $950.99   $951.00   $951.00